Power distribution circuits provide power to other circuits, and protect both the power source and load of the power distribution circuit from an over-current fault. These circuits, which are also referred to as soft-switches, hot swap controllers, or electronic circuit breakers, provide on/off control, inrush control, and over-current protection. Typically, one or more power metal-oxide-semiconductor field-effect transistors (MOSFETs) and control circuitry are provided.
By way of example, in power systems for high-density servers, high voltage DC power distribution is controlled with electronic switches (e.g., MOSFETs) to isolate load faults and to provide desired system availability. Since loads of the MOSFET circuit are typically capacitive, high power dissipation can occur when a MOSFET is first enabled. If the MOSFET(s) is soft-started, then simultaneous current and voltage drops occur. This high power and energy through the MOSFET can cause the MOSFET to fail.
Two different approaches exist to making a power distribution circuit more robust; that is, use of a customized soft-start circuit or a pre-charge circuit. With customized soft-start circuitry, during soft-start, the main switching MOSFET is in the linear region of operation. However, advances in MOSFET technology, such as high transconductance, optimize switching performance, while sacrificing linear region robustness. Thus, is it increasingly difficult to find MOSFETs suitable for linear mode operation. One particularly beneficial soft-start approach is described in commonly assigned, U.S. Pat. No. 7,741,821 B2. In the conventional pre-charge circuit approach, the load side of the one or more switching MOSFETs of the power distribution circuit may be pre-charged through a startup resistor. An additional startup MOSFET may also be used to enable the startup resistor. In operation, this startup MOSFET is typically switched on instantaneously, thus avoiding linear mode operation. Disadvantageously, today's pre-charge circuits can be complex, costly, and large.